Neutron Stars 4: Magnetism. Andreas Reisenegger ESO Visiting Scientist Associate Professor, Pontificia Universidad Católica de Chile. Bibliography.
ESO Visiting Scientist
Pontificia Universidad Católica de Chile
Caution: Little is known for sure – many speculations!
Spin-down time (age?):
Kaspi et al. 1999
Pure toroidal & pure poloidal field configurations are unstable, but in combination they can stabilize each other.
(Simulations: Braithwaite & Spruit 2004)
requires internal field ~10x inferred dipole
Result of accretion?
progressive increase of inferred B
X-ray pulsars: magnetic chanelling of accretion flow
Cyclotron resonance features B=(1-4)1012G
Low-mass companion (LMXB):
Likely old (low-mass companions, globular cluster environment)
Mostly non-pulsating (but QPOs, ms pulsations): weak magnetic field
Alfvén radius: Balance of magnetic vs. gravitational force on accretion flow
circled: binary systems
Manchester et al. 2002
Can the field of MSPs have been transported onto them by the accreted flow?
(Goldreich & R. 1992)
NS core is a fluid mix of degenerate fermions: neutral (n) and charged (p+, e-)
Chemical equilibrium through weak interactions, e.g., p++ e- n + e density-dependent mix.
Stable chemical stratification (“Ledoux criterion”), stronger than magnetic buoyancy up to B ~ 1017 G.
To advect magnetic flux, need one of:
Real-time adjustment of chemical equilibrium
“Ambipolar diffusion” of charged particles w. r. to n’s (as in star formation).
Protons & electrons move through a fixed neutron background, colliding with each other and with the background (Goldreich & Reisenegger 1992):
Time scales depend on B (nonlinear!), lengthscales, microscopic interactions.
Cooper pairing (n superfluidity, p superconductivity) is not included (not well understood, but see Ruderman, astro-ph/0410607).
Assume that the only mobile charge carriers are electrons (solid neutron star crust or white dwarf):
“Electron MagnetoHydroDynamics” (EMHD)
Biskamp et al. 1999: w(x,y)=2Bat 3 different timesin 2-D simulation.
Vainshtein et al. (2000):
Our recent work
(paper in preparation):